The easiest way to learn is through practice practice and more practice, having someone experienced on hand to help you.
Depending on what type of bandages you are using, please use pads underneath to help prevent bandage bruising from pressure points.
I bandage on about a 45 degree angle, starting in the middle of the leg, working down to just below the fetlock, and back up to just below the knee. The more you practice the better you will get at finding exactly the right tension to apply when you bandage. Too loose and they'll slip down (can be very dangerous if they slip to the hoof!), too tight and they can cause big tendon problems and bandage bruising.
Really, unless you HAVE to bandage, don't bother. Boots are far easier and more food proof. I only bandage for interstate/international clinicians, and presentation if selling a horse.
That said, its still a good skill to put away in your 'toolbox'